The goal of these studies was to elucidate the participation of hormones and the second messengers cyclic 3',5'-adenosine monophosphate (cAMP) or cyclic 3',5' guanosine monophosphate (cGMP) in the regulation of tyrosine hydroxylase biosynthesis in sympathetic ganglia and adrenal medulla. Our studies how that at least 3 types of receptors (beta-adrenergic, nicotinic and corticosterone receptors) are involved in the induction of tyrosine hydroxylase in superior cervical ganglion. Our findings also demonstrate that an alterated cAMP/cGMP ratio may represent the second messenger response to the stimulation of these different receptors. Considering the antagonistic role that cAMP and cGMP exerts on the gene expression in several cellular systems we plan to study if the cyclic nucleotides, through protein kinase interacting with repressor proteins in the nucleus, stimulate RNA transcription.